1. Field of the Invention:
The present invention relates to an oil-level sensing apparatus, and more particularly to an oil-level sensing apparatus in an engine for a motor vehicle.
2. Description of the Related Art
A conventional sensing apparatus for the oil-level in an engine is disclosed in the "MERCEDES BENZ" Service Manual published in 1985 in the U.S.A., and is shown in FIG. 5. Therein, a housing 81 of a sensing apparatus 80 is fixed to an oil-pan 82 of an engine (not shown). A float-guide 83 is fixed to the housing 81, and a reed-switch 84 is inserted therein. A float 85 is located around the float-guide 83, and is moved upwardly or downwardly according to the oil-level in the housing 81. A ring-shaped permanent magnet 95 is fixed in an inner circumferential portion of the float 85.
A first communicating port 86 is formed in the lower portion of the housing 81, and a second communicating port 87 is formed in the upper portion of the housing 81. The communication between the inside of the housing 81 and its outside is established by the first communicating port 86 and the second communicating port 87. Therefore, oil in the oil-pan 82 flows into the housing 81.
The center portion of a plate 88 is fixed to the housing 81 so as to open or close the first communicating port 86. The plate 88 performs a snap-action to open or close the first communicating port according to the temperature of the oil in the housing 81.
A pair of lead-wires 89, 90 are connected with the reed-switch 84. The lead-wire 89 is connected or grounded with the earth E. The lead-wire 90 is connected with the earth E via an electric delay unit 91, an indicator lamp 92, an ignition switch 93 and a power source 94, all of which are connected in series.
In the above oil-level sensing apparatus, when the engine is started by turning on the ignition switch 93 while the temperature of the oil is lower than 60.degree. C., the plate 88 is in a closed state to close the first communicating port 86. Therefore, the oil-level in the housing 81 is not varied even if the oil-level in the oil pan 82 is varied. This is provided due to the fact that when the temperature of the oil is low, the viscosity of oil is high, so that oil slowly circulates in the engine. Thus, the oil-level in the oil pan 82 decreases with time, even though the quantity of the oil does not actually decrease. Therefore, when the temperature of the oil is low, the sensing apparatus 80 does not act.
On the other hand, if the temperature of the oil is higher than 60.degree. C., the outer circumferential portion of the plate 88 opens to open the first communication port 86 (FIG. 5), so that the fluid communication between the inside of the housing 81 and the outside thereof is established.
Therefore, the oil-level in the housing 81 becomes equal to the oil-level in the oil-pan 82. If the oil-level in the oil-pan 82 is sufficiently high, the float 85 is located at an upper portion of the housing 81. Thus, the reed-switch 84 is not influenced by the magnetic flux of the permanent magnet 95 and remains open, so that the indicator lamp 92 is located in the open-circuit and is not turned on.
If the oil-level in the oil-pan 82 is low, the float 85 is located at a lower portion in the housing 81. Thus, the magnetic flux of the permanent magnet 95 brings the reed-switch 84 into a closed condition, and the circuit is closed to thereby light the indicator lamp 92.
If a vehicle (not shown) powered by the engine suddenly starts, stops or turns, the oil-level in the oil-pan 82 is temporarily lowered. The float 85 follows the oil-level, so that the reed-switch 84 is closed. The signal of closure of the reed-switch 84 is delayed about 30 seconds by the electric delay unit 91. After that, if the reed-switch 84 remains closed, the indicator lamp 92 is turned on. Therefore, the indicator lamp 92 is not turned on when the oil-level in the oil-pan 82 is only temporarily lowered. However, the electric delay circuit increases the cost and complexity of the unit.